Numerous heterogeneous contacting methodologies have been used, including chemically reactive and adsorptive methodologies, for the real-time removal of contaminants and toxins from liquid, gaseous and air streams. These contacting methods include fluid beds, ebulated beds, trickle beds, monoliths and packed beds, among others. Among the best known of these is the packed bed which incorporates particulate matter within a containment vessel through which a contaminated liquid, gaseous or air stream is passed. One example of such a packed bed was the filter on the World War I-era gas mask carried by U.S. military personnel. Within each filter were a pre-defined thickness of compacted particulates of charcoal and other reactive materials for the removal of any toxins passing therethrough. While such methodologies were effective they suffered from numerous inefficiencies that limited the useful lives and performance attributes of the filters. Many of these inefficiencies remain in the present day methodologies used to remove a wide range of contaminants and other harmful agents from a variety of liquid, gaseous or air streams.
One example of the applicability of the present invention involves the preferential oxidation (PROX) of CO from streams comprised predominantly of H2. Such processing and treatment methodologies are believed to be the most efficient way to remove CO from practical hydrocarbon reformate streams for use by poison intolerant Polymer Electrolyte Membrane (PEM) fuel cells or SOFC fuel cells for example. Pt/Al2O3 has long been known as a suitable catalyst for this purpose. Over conventional Pt/Al2O3 catalysts, however, preferential oxidation of CO in H2 is known to occur only to a significant extent at temperatures above 150° C., and the maximum CO conversion usually takes place at around 200° C. With the present invention, modification of Pt/Al2O3 with a transition metal promoter may result in significantly enhanced catalytic performance for preferential CO oxidation from practical reformates in the temperature range of 25 to 150° C. This lower reaction temperature, and the maintenance of high selectivity toward CO oxidation rather than H2 oxidation, permits the associated filter element to operate at the PEM fuel cell stack temperature (or become an integral portion of the stack) in the absence of additional process controls and associated hardware.
Limited contacting efficiency with the liquid, gaseous or air stream, low chemical conversation rates, limited heat and mass transfer through the filtration system, inability to regenerate, high weights, extremely limited duration of effectiveness, ineffectiveness at relatively low temperatures, and large pressure drops are among the numerous problems identified with prior art reactive filtration systems. It is, therefore, desirable to provide a multilayer microfibrous filtration system with entrapped reactive materials, including heterogeneous catalysts, electrocatalysts, sorbents, and various other solid reactant materials for the removal of contaminants and other harmful agents from a liquid, gaseous or air stream.